Fabrication of schottky diodes on n-type GaAs

Abstract

Ohmic contacts on the n-type GaAs were formed by the sequential deposition of metals. Ni, Ge and Au or Ni and Au-Ge eutectic was sequentially deposited on the n-type GaAs wafers and they were alloyed at temperatures ranging from $380\,^\circ\!C$ to $470\,^\circ\!C$. It was found that the characteristics of the alloyed ohmic contact was more linear and its resistance was smaller than the non-alloyed one. It was assumed that Au enhanced the out-diffusion of Ga and that Ni enhanced the in-diffusion of Ge. Ge can take the Ga sites substitutionally and then degenerate n$^+$ layer can be formed. These n$^+$ layers make ohmic contacts through tunneling mechanism. In order to prepare a GaAs surface as clean as possible, the etching should be performed at low temperatures. The each rate of GaAs crystal with the combination of $H_2SO_4,\; H_2O_2$ and $H_2O$ increased as the portion of $H_2O_2$ in the etchant increased. The Au, Cr and Al Schottky diodes on the n-type GaAs that has dopant concentration of $2\times10^{18} cm^{-3}$ were fabricated using the lift-off technique in which the AZ-1350J positive photoresist was used. The lift-off technique became easier by the soak into the chlorobenzene because the soak made the negative slope (overhang). The fabricated Schottky diodes shows high ideality factors and it was believed to be due to poor surface treatment.